At some point, if you have confidence in the mechanics doing the work, you will have to let them make decisions. If you do not have any confidence, that's a problem since you will not be able to train them with second hand information.
I'm not digging up information to second guess the mechanics here - I am doing it because I am loving learning about the inner workings of our engine. It is a wonderful beautiful machine - and we are loving the chance to literally see and touch every single piece of it.
I love being able to actually refer to books, wisdom and experience.
As luvrbus said - five different DD guys might give five different answers. It is interesting to learn how they came to their conclusions, and to learn from their years of experience. This is exactly why I love having luvrbus on the forums, and I love that so many other experts are willing to share their experience and wisdom here and via phone.
Learning about these engines is a blast - that is why we are nuts, right?
I hope that this is not one of those shops that posts an hourly rate, a higher one if you watch, and a higher one if you offer suggestions.
Actually - much to our delight this shop has been incredibly welcoming, inviting us to watch, and going out of their way to not just show us everything but to explain the inner workings. They love that we are so interested, and they encourage us to tap into other experts and they are eager to hear what we learn.
They have capped the number of hours on the estimate too, so they are not running up the clock in the process - and they even lowered their hourly rate & hours when they gave us the final quote.
And they have given us access to tools and equipment and help for tackling a few other projects while we are here too.
Overall I couldn't be more pleased with this shop. They aren't the cheapest, but they are being extremely thorough, and providing us an invaluable education too.